The goals of the project are to evaluate the effect of Trigeminal Tractotomy (and other lesions) on the behavioral and neurophysiological responses of Macaque monkeys to electrical stimulation of the dental pulp and to determine what modifications in such responses result from administration of certain drugs. The results of the first year's activity may be summarized as follows: a. Trigeminal tractotomy does not produce analgesia to electrical stimulation of dental pulp in the macaque. b. Following tractotomy animals showed no behavioral response (presummed analgesia) to pinprick in the peripheral portion of the face. Near the midline, adversive responses were present and either normal in intensity or slightly decreased compared to the unoperated side. Intraoral responses to pinprick correlated with midline cutaneous responses. c. Subconvulsive doses of Strychnine (25 mg kg) given intramuscularly had no effect on dental escape thresholds, but analgesia to cutaneous pinprick was abolished by Strychnine. Oral L-Dopa (50 mg kg) produced similar but less reliable responses than Strychnine. For the coming year we plan to complete behavioral studies relating to the effects of combined tractotomy-rhizotomy lesions on dental and orofacial sensation. Further, we plan to include Methyl-Dopa and 20 percent nitrous oxide in evaluation of pharmacological manipulation of orofacial sensation. Our major thrust in this second year will be to accumulate physiological data to correlate with the behavioral studies. The four animals now under study will be utilized for this purpose as will 4-6 new animals.